Submitted to: Journal of Eukaryotic Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/1996
Publication Date: N/A
Interpretive Summary: Microspora (Protozoa) is a large group of pathogens with some species that infect beneficial insects and others that destroy important insect pests. A new infection starts by the hatching of the spore in the host gut. Studies of matters as diverse as host specificity, spore dormancy and spore survival in nature and during or after formulation will be enhanced by basic knowledge about how the spores hatch. The latest theory about ho microsporidian spores hatch supposes that water enters the spore to increase internal pressure but, because spores hatch so quickly, it has never been observed. This study, for the first time actually measures the uptake of water during the hatching process. This was done by substituting heavy water (D20) for normal water and using chemicals that are known to affect water channels in the membranes of other cells. The results ob- tained suggest that spore hatching is dependent upon the hydration states of the cell wall, cell membranes and the stimulant ions. It also demon- strated that water flows into the spores through specific channels in the cell membrane, analogous to the water channels by which water moves through the outer membranes of other cells that are known to be highly permeable. This knowledge will be useful, primarily to other scientists. Interaction between the spore and its environment revealed through this research will assist those working with microsporidia in their efforts to destroy spores that infect economically important insects or, alternatively, maintain spores alive through harvesting and formulation for biological control of insects.
Technical Abstract: The germination of microsporidian spores under conditions expected to affect water flow across the plasma membrane-wall complex was studied by assessing their responses to in vitro stimulation with Na+ or K+. Partial or full substitution of common water with D2O delayed and inhibited spore germination in a concentration-dependent manner, but pre-incubation in 100% D2O did not change the normal response to standard stimulation. Water structure-breaking conditions, such as an increase in temperature (within the 15 to 40 degrees C range) or in ionic strength (2 to 10-fold normal), opposed the inhibition by D2O and allowed significant stimulation by Li+, the monovalent cation with the largest hydration diameter and weakest stimulant action on the spores. Ethanol, known to reduce water permeation across cell membranes, also caused a powerful and dose- dependent inhibition of spore germination but pre-treatment with ethanol did not affect the normal response. HgCl2, an inhibitor of specific water channels, blocked spore germination at just 250 micro- Meters in the normal stimulation solution irrespective of the temperature, and permitted only a quite delayed response in high salt stimulation solutions. Inhibition by Hg2+ was abolished by the simultaneous presence of 2-mercaptoethanol in the medium. These results suggest that germination is dependent upon the hydration states of the plasma membrane-wall complex and the stimulant ions, and that osmotic water enters the spores through specific channels with critical sulfhydryl groups, analogous to the water channels in other permeable cells.